We know that Cyndane's raw strength is less than Lanfear's full potential. And that THAT strength was described as incredibly powerful when first seen at the Forsaken meetings in earlier books, when the Forsaken 'sensing' her did not yet know who she was for certain.

If she is now under some other kind of restriction, that would be what placed her underneath Nynaeve and others... but the original assessment of Cyndane's power was much higher than what is being described here.